This invention relates to liquid crystal displays (LCDs) and more specifically to temperature compensating drivers for LCDs.
LCDs are well known in the art. A typical LCD includes a back plane coupled to a back plane lead and eight segments, each segment being coupled to an associated segment lead. When the voltage at a given segment lead exceeds the voltage at the back plane by a predetermined threshold voltage, the associated segment is dark and therefore visible. Similarly, if the voltage at the back plane exceeds the voltage at the segment lead by the predetermined threshold voltage, the segment is dark and therefore visible. However, if the voltage at the segment lead equals the voltage at the back plane, the segment is transparent and therefore not visible. The eight segments are typically arranged so that any of a number of alphanumeric characters can be displayed by selectively darkening various combinations of segments.
Another type of LCD is the biplexed LCD. A typical biplexed LCD includes sixteen segments and two back planes, each segment being associated with one of the two back planes. Each back plane is coupled to an associated back plane lead. In addition, a typical biplexed LCD display includes eight input leads, each input lead driving two segments. Each segment is either dark or transparent depending upon the difference in the voltage at its associated input lead and its associated back plane.
The above-mentioned threshold voltage is greater at low temperatures than it is at high temperatures. According, it is desirable to drive LCDs with greater voltages at low temperatures in order to ensure that the display segments darken properly. Similarly, it is desirable to drive LCDs with lower voltages at high temperatures to avoid cross talk. (Cross talk occurs when a display segment is darkened by an attempt to darken a different display segment.